their Secretions, 629 



a species of /Salpa, Mr. Beaufort informs us it gave no light 

 unless the water was violently agitated. " On holding one 

 in my hand," he adds, " and gently pressing it, a faint flame 

 seemed to pervade the whole inside ; and on each projecting 

 point there seemed to stand a little globule of very vivid 

 light. On increasing the pressure, its brilliancy likewise in-» 

 creased for a few moments, then gradually declined for some 

 time, as if exhausted by the exertion. It may have been 

 fancy, but, at the time, I was convinced that it gave out 

 a sensible degree of warmth to the hand." (Home' ^Lectures, 

 vol. i. p. 367.) The latter observation is probably not fanciful, 

 but real ; for the great Humboldt has proved that the »Salpae 

 (Biphora of the French), as well as the Pyrosomae, when pre- 

 served in a bottle, make the temperature of the water rise 

 nearly one centigrade degree. The same naturalist, so re- 

 markable for the extent and universality of his knowledge, 

 tells us that the Pyrosoma atlanticum diffuses, " while swim- 

 ming beneath the surface of the sea, a light of a foot and a 

 half in diameter. Only imagine the superb spectacle which 

 we enjoyed some days ago, when, in the evening, from seven 

 to eleven o'clock, a continuous band of those living globes of 

 fire passed near our vessel. With the light which they dif- 

 fused, we could distinguish, at a depth of 15 ft., the individuals 

 of Thynnus Pelamys, and ASardon, which have followed us 

 these several weeks, notwithstanding the great celerity with 

 which we have sailed." {Edin, Phil. Journ.^ vol. xii. p. 1S5.) 

 Mr. Thompson has given an interesting account of the same 

 species. It presents itself to the astonished voyager, in the 

 calm latitudes near to the line, under the appearance of thick 

 bars of metal of about half a foot in length, ignited to white- 

 ness, scattered over the surface of the ocean. Some assume 

 the luminous state, and continue so as long as they remain in 

 view ; while, in others, the luminosity declines and disappears. 

 — " The greater number of these apparently incandescent 

 masses pass close to the sides of the vessel, or follow in her 

 wake ; their phosphorescence being called into activity by 

 coming in contact with her prow or bottom, as that of such 

 as are more distant appears to be, by the conflict of the 

 waves." The light appears to pervade the whole substance 

 of the animal, and, " when examined near at hand, varies in 

 intensity and in shade, often exhibiting a very beautiful 

 phosphorescence of a bluish or greenish tinge, like a pale 

 sapphire or aquamarine, as it gradually fades away. Agitation 

 or friction renews it, as in other luminous animals, as long as 

 it continues to exhibit signs of life ; but it is most vivid when 

 the animal is first drawn up, and at length can sgarcely be 



s s 3 



